Manufacture of artificial filaments or threads



Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE MANUFACTURE OFARTIFICIAL FILAMENTS R THREADS Henry Dreyfus, London, England NoDrawing. Application January 4, 1929, Serial 7 N0; 330,408. In GreatBritain January 23, 1928 Claims.

:glycols or other polyhydric alcohols, or other organic derivatives ofcellulose capable of being formedinto artificial filaments bydry-spinning methods. a i

In U. S. Patents Nos. 1,602,125, 1,541,104 and 1,731,318 processes andapparatus for the production of artificial filaments or fibres aredescribed, in which a solution of cellulose acetate orother cellulosederivative in a volatile solvent liquid is extruded through spinningjets into chambers, through which passes an evaporative medium such asair or other inert gas. These patents include the fundamental advancesin the art of dryspinning artificial filaments which have rendered itpossible at the present day to manufacture dry-spun cellulose acetateartificial silk of any required denier and of the highest commercialquality, both in regard to strength andlustre and in regard touniformity, and particularly to uniformity in dyeing properties, thelast-mem tioned being of the greatest importance for the production oftextile fabrics dyed to an absolutely uniform tint throughout the piece.Briefly stated, the improvements in question comprise the use ofspinning chambers or cells coupled with outside winding or spinning ofthe filaments when associated into threads, the combination therewith ofcap-spinning devices, the provision of means for oiling, lubricating ormoistening the threads as they pass to the cap-spinning devices, and,most important of all, the provision of means for securing a uniformfiow of air or other evaporative medium through each of the spinningchambers or cells, and subsidiary thereto, means for adjusting the heatsupply so as to obtain uniform temperature conditions in each of thespin- The higher the denier and the greater the speed, 7

the larger is the amount of air or other gas used.

; The speed of the evaporative medium is regulated (CI. 18-54) a inaccordance with the principles laid down in U. S. Patent No. 1,541,104so as to give a regular production of filaments or threads in each cell,in the cells of each spinning metier, and also in V the total number ofmetiers used for the manufacture of threads of thesame denier. Further,it becomes practicable by adjustment of the flow of the air or other gasto spin different deniers in different metiers and even in differentcells of the same metier, as desired. The heat supply is 10 controlledto give uniform temperature conditions in each cell, this adjustmentbeing dependent on the regulation of the flow of air or other gas, thelatter being of primary importance in securing really uniformtemperature conditions.

At the same time the speed of the air or other gas must be adjusted togive such a concentration of the solvent vapours carried away by the airor other gas that the recovery. of the solvent is economical, the amountof air or other gas used being adjusted accordingly in accordance withthe amount of solvent evaporated.

The temperatures chosen for spinning are likewise of a definite nature.In order to get the usual lustrous commercial threads,.as'producedaccording to the previously mentioned patents,

the temperatures employed for a given denier and 50 and 90 when one usesacetone or acetonealcohol mixtures as solvent. When one uses anacetone-alcohol mixture, the spinning temperature is naturally higher,as a liquid of higher boiling point has to be evaporated; the greaterthe quantity of the latter, the higher the temperature must be.

If, however, lower boiling solvent liquids than acetone oracetone-alcohol mixtures are used, for example, if the acetone isreplaced by lower boiling solvents. such as methyl formate or if ethylalcohol is replaced by methyl alcohol the temperature will beaccordingly lower. Again,the

temperature varies according .to the denier spun,

a lower denier requiring a lower temperature. Also, the higher the speedof the air or other gas used for spinning the lower the temperature maybe. Further, if a higher or very high temperature is chosen, then thespeed of the air or other gas may be less. That is to say, there is aninter-relationship between the different variables. and What it amountsto is that it is the total quantity of heat supplied per unit of timewhich counts and nothing else. As the rate at which heat is supplieddepends on the speed of the air or other evaporative medium, theimportance of the improvements comprised in U. S. Patent No. 1,541,104will be at once apparent, since they enable the air speed to be adjustedaccording to the denier spun and the temperature adopted and accordingto the requirements of any particular spinning solution, whether itcomprises a single solvent or a combination of solvents.

For each particular solvent or solvent mixture used, the limits withinWhich the filaments are more or less lustrous or even dull, according torequirements, are relatively narrow and can be easily adjusted by anadjustment of the speed of the evaporative medium by the means describedin the afore-mentioned patent. Indeed, no method based on any otherprinciple of controlling the operation of dry-spinning plant has yetbeen suggested, which permits the temperature, the denier spun, and thespeed of the air or other gas, which last-mentioned indirectly governsthe temperature, to be properly adjusted in their closeinter-relationship according to requirements.

The limits between which the flow of the air or other evaporative mediumcan be varied are also controlled in practice by a number of otherconsiderations. Thus, the adoption of a substantially increased airspeed means the dilution of the solvent vapour to such an extent thatits recovery may become uneconomical and for this reason it is advisableto keep within certain limits. It is also important, in using solventswhich are inflammable, to keep the concentration of solvent vapourWell-below the limit at which explosive mixtures with air are formed.

When filaments produced by the foregoing methods are examined, it isfound that they are to some extent cellular or tubular, and that themore voluminous they are in character, the more pronounced is theircellular or tubular structure. 50

This is especially the case when spinning solutions of lowerconcentrations are employed, e. g.

when the solutions contain 10% to 20% of cellulose acetate instead ofconcentrations of 25-30% such as are prescribed in U. S. Patent No.1,688,351. The cellular or tubular structure of the filaments moreoveris developed to a larger extent when a high spinning temperature isadopted in order to get .a highly lustrous thread.

In the making of viscose in the past substantial quantities of carbonbisulphide have been used, which still remain in the spinning solutiontogether with all sorts of decomposition products of a gaseous nature,such as sulphide products, especially sulphuretted hydrogen, which areformed in the spinning solution both before and during the coagulation..The presence of these substances in the spinning solution has enabledalready'the production of fibres of a more or less cellular or tubularcharacter. The cellular or tubular fibres produced in this way were onlyobtained to a limited extent, and did not attract any special notice,untilefforts were made to produce so-called hollow'filaments, when itwas suggested tointroduce air or gases into the spinning solutions inorder to produce these hol low fibres.

Attempts have also been made to produce hollow filaments by introducinginto the spinning solutions small quantities of gases or non-solvent 5gas-producing liquids, which upon the application of heat should produceindustrially valuable hollow fibres. These methods are incapable ofapplication to spinning solutions containing cellulose acetate or othercellulose derivatives, and especially to the production of filamentsfrom such solutions by evaporative processes. On the one hand either thesaid gases or liquids cannot be introduced into the spinning solution insuflicient quantity or be distributed therein with suiiicient uniformityto give the desired result, or on the other hand, if they are misciblewith the spinning solution in sufiicient quantity, they act asprecipitants for the cellulose acetate or other cellulose derivative,thus making spinning impossible.

In order to produce fibres of the expected strength and desired denier(and especially of low denier) and anyhow filaments of increasedhollowness as compared with the filaments previously produced, it isnecessary to incorporate in the spinning solutions used in thedry-spinning process very large quantities of real solvents as themedium for the formation of the cellular or tubular structure, so thatthey realy constitute the medium for the production of the spinningsolution. That is to say, it is necessary to proceed on quite adifferent basis from the previous attempts, where small quantities ofair or gases or insoluble liquids were used for the purpose of producingthe desired effect.

In the spinning of nitrocellulose, solvents such as ether are used insubstantial quantities and yet one does not get the formation of tubularor cellular threads to such an extent that they are different from thethreads produced in normal dry-spinning operations. It might be expectedthat, if small quantities of air or gases or indifierent volatileliquids give such an effect, a very volatile solvent like the etheremployed in nitrocellulose manufacture, especially as it is employed insuch large quantities, would be much more likely to produce the efiectof hollowness. However, as will be explained hereafter, quite differentconditions are necessary in order to get increased cellular or tubularfilament formation.

Hollow filaments can, it is true, be produced from the usual spinningsolutions by the use of spinning temperatures substantially higher thanthe boiling points of the solvent, coupled with a very substantiallyincreased rate of flow of the air used as evaporative medium. Whilst itis a fact that, in using very substantially increased temperatures and arapid air flow as stated, hollow fibres can be produced, difiiculty hasbeen experienced in drawing out these hollow fibres to lower deniersthan about 15 to 10, on account of troubles due to breakage during thespinning operation. The reason for this is easily understood when oneconsiders that the operation of forming the filaments at a very muchincreased temperature and air speed involves a rapid elimination of thesolvent in the filaments, which, naturally, as the solvent tries toescape, weakens or bursts the skin or surface of the filaments soformed. This may affect both the coherence of the filaments and theirstrength. As a result of the quick elimination of the solvent, which isthe characteristic feature in the production of so-calledhollowi"filaments, the filaments become dry so quickly that there is notime for drawing them' out to low deniers'before they reacha conditionin which the filaments are liable to break.

It has now been found, according to the present invention that, withoutrelying on the spinning conditions above mentioned of substan-. tiallyincreased spinning temperature and rapid air speed, it is possible, byadopting-the conditions hereinafter described, to produce threads ofcellular or tubular character, as required, and also of across-sectional area which can be regulated according to requirements bythe observance of the special conditions hereinafter described. Theseconditions give filaments of the desired increased volurninosity whichcan be drawn out to any filament denier, according to requirements. Thesaid filaments can be pro-' duced on a commercial scale withoutinterruption and have a strength comparable with the strength of thefilaments spun under normal conditions, that is to say, when lesscellular filaments are formed. For example, if a cellulose acetate of acertain viscosity is chosen which is supposed to give undernormalconditions a certain strength, it would according to the presentinvention give about the same strength. This means in other words that,if a cellulose acetate of very high viscosity is chosen which givesunder normal conditions a very much increased strength, voluminousfilaments of similar strength can be obtained according to the presentinvention; also if an acetate of low viscosity is takenwhich gives undernormal conditions filaments of lower strength, a corresponding lowerstrength can be obtained when filaments of cellular or tubular form areproduced according to the present invention, and not a relativelyreduced strength as when a spinning temperature very substantiallyhigher than the boiling point of the solvent and a very much increasedair speed are used. In the above discussion, whether based on theproduction of defective cellular or tubular filaments in one way or theother according to the prior art, or based on the production of threadsaccording to the methodtwhich is the object of the present invention, itis assumed that the filaments are produced under the best conditions,namely, according to U. S. Patents Nos. 1,602,125 and 1,541,104, asotherwise the filaments would show irregularities from cell to cell orin themselves, unlessthe flow of air or other evaporative medium werecontrolled in aregular manner as described in U. S. Patent No.1,541,104, whether the filaments were spun at ordinary temperature orwith heat at a temperature appropriate to the speed of the air or othergas.

The present invention consists primarily in a process for themanufacture of voluminous filaments or fibres of a more or less cellularor tubular, or continuously tubular character, consisting in dryspinning solutions of celluloseacetate or other cellulose derivativesdissolved in a solvent mixture containing atv least two volatileconstituents in proportions such that the lower boiling constituentvaries from a major part of the solvent mixture to a minor according asthe boiling point difference of the said constituents is small or great,the boiling points, moreover,,dif-

fering by such an amount that filaments QrLfibres of the desiredcharacteristics as to volurninosity are produced at spinningtemperatures below .or at any ratenot substantiallyabove the-[boilingpoint of the higher boiling of said constituents;

' filaments produced in normal spinning, and cavoluminous filaments of amore or less cellular or tubular or completely tubular character can beproduced under these conditions, said filaments having about the'samedegree of strength as the pable of being drawn out to low or lowerdenier as desired. By varying the temperature, it is possible to passfrom the normal filaments produced at temperatures slightly above theboiling point of the lower boiling constituent of the solvent 10 mixturethrough stagesin which the filaments are, first partly cellular, and,then, uniformly cellular or partly tubular, to the stage at which thefilaments are completely tubular. At the maximum temperature, thefilaments are com- 15 pletely tubular, cellular filaments being obtainedat lower temperatures which are at the same time substantially higherthan those at which normal filaments are produced.

The spinning temperature varies in accord- 20 ance with the proportionof the lower boiling constituent; the greater the quantity of lowboiling constituent, i. e. the lower the quantity of high boilingconstituent, the lower may be the spinning temperature. 25

The substances constituting the solvent mixture may each be solvents forthe cellulose acetate or other cellulose derivative or one or both ofthem may be diluents or non-solvents provided that together they form asolvent mixture. Thus, 30 alcohol-benzol mixtures may be employed assolvent, or mixtures containing a solvent, such as acetone, togetherwith small quantities of a nonsolvent, such as water.

The best results are obtained by the use of 36 constituents having aboiling point difference of not less than to'50 C., and preferablybetween 50 or 60 and 100 C. or higher.

As stated above, the proportion of low boiling constituent to highboiling constituent varies 40 with the diiference in their boilingpoints. The smaller the boiling point difierence, the larger must be theproportion of the low boiling constituent. If the boiling pointdifference is under 40 C. the quantity of the lower boiling constituentused should be at least or and preferably 75% or more of the totalamount of the solvent mixture used. When the difference in the boilingpoints of the two constituents is between 40 and 50 C. the quantity oflower boiling con- 50 stituent used is usually higher and preferablysubstantially higher than the quantity of the higher boilingconstituent.

. It will be understood that, subject to the above considerations, it isalso possible by adjusting the 5 proportions of the constituents of thesolvent mixture to vary to some extent the voluminosity of the filamentsso as to produce filaments of a more or less cellular or tubular orcompletely tubular character. Q

The 'voluminosity or volume oi the filaments is increased and theapparent density is diminished by selecting appropriate conditions, suchas more dilute spinning solutions and/ or the employment of plasticizersand/or a spinning temperature 51* which is of such a nature that thehigher boiling liquid evaporates at such a rate as to enable thefilaments under formation to retain suflicient extensibility until theyhave achieved the desired highest volume coupled with the thinnest skinC formation. The volume of the filaments can be diminished by usingopposite conditions to those employed for getting the greatest volume.

The speed of the air or other evaporative medium usedis adjustedaccording to the denier 75.,

happens, a liquid, which when used by itself is a the filaments as aplasticizer.

spun (i. e. the higher the denier spun, the more air is used), accordingto the spinning speed employed (i. e. the greater the spinning speed,the greater the amount of air used), and according to the concentrationof the spinning solution (1. e. the higher the concentration of thespinning solution, the less the air speed). The speed of the air orother evaporative medium must also be adjusted together with thetemperature used in order to ensure the supply of the requisite heatunits, and to enable a uniform grade of filaments to be obtained in eachcell of each metier and in all the metiers used.

As a further example of the way in which the spinning factors arerelated, it may be stated that the lower the denier and the lower thespinning speed, the lower need be the difference in the boiling pointsof the liquids in the solvent mixture, also the less may be the quantityof lower boiling liquid as compared with the higher boiling liquid.

The said constituents of the solvent mixture, having as previouslyexplained, a certain definite difference between their boiling points,and pref erably a difierence of 50 or 60 to C. or substantiallymore-though the difference may be less, provided that the proportions ofthe constituents are suitably adjusted-may each be a mixture of liquids.Thus the lower boiling solvent may be a mixture of solvents just as thehigher boiling solvent may be a mixture of solvents. Further, in thelower boiling solvent and/or the higher boiling solvent some diluentsmay be contained to a certain degree, or, as often so-called diluent,may be combined with another diluent or even with a nonsolvent to form asolvent mixture. For example, alcohol, which is practically not asolvent, may become a positive solvent when used together with acetone;similarly alcohol together with benzol is a solvent, and water can beused with acetone as solvent.

The solvent mixture employed may also contain, in addition to theessential constituent liquids of widely separated boiling points,solvents and/or diluents, having an intermediate boiling point betweenthe boiling points of the said liquids. In such case, it is advisable toadjust the quantity of the higher boiling liquid or solvent, or to use,in addition, a corresponding quantity of a still higher boiling liquidor solvent so as to establish the necessary equilibrium. The spinningshould take place at a temperature lower than the boiling point of thehigher boiling liquid or solvent, or anyhow not substantially higher, soas to produce voluminous, more or less cellular or tubular filaments aspreviously explained. V

The higher boiling constituent of the solvent mixture may eitherfunction as volatile solvent as explained aboveprovided the spinningtemperature chosen is sufficiently high to ensure the elimination of thesaid higher boiling constituent-or it may function partly as solvent andpartly as plasticizer when lower spinning temperatures are used; andespecially in the case when the difference between the boiling points ofconstituent liquids is very great, and a certain amount of the higherboiling solvent remains in In this case it is advisable to adopt ahigher spinning temperature, so that the higher boiling solvent remainsto an amount substantially under 100%, and preferably to the extent. ofonly 50-5% orless,

calculated on the weight of the cellulose derivative.

True'plasticizers, as distinguished from high boiling volatile solvents,may also be incorporated in the solvent mixture. If plasticizers of veryhigh boiling point e. g. -200 or over, are employed, such as methyl orethyl xylene sulphonamides or mixtures thereof, then in order to formthe threads with the requisite coherence and strength, it is necessaryto use not more than 50%, and preferably 20-5% or less, calculated onthe weight of the cellulose derivative. The plasticizer can afterwardsremain in the filaments where the qualities imparted to the thread bythe plasticizer are useful in the subsequent textile operations, or, ifnecessary, it may be removed by extracting it with a solvent for theplasticizer, which at the same time is nota solvent for the silk, or itmay, as in the case of some of the xylene sulphonamides, for instance,be washed out with chemicals such as dilute soda solution or sodiumbicarbonate solution.

In order to illustrate the principles of the invention, it will now bedescribed in its application to specific combinations of liquids to formthe solvent mixture used for spinning cellulose acetate.

If acetaldehyde (boiling point 21 C.) (preferably in a stabilized form,in which polymerization is prevented in known manner) and acetone(boiling point 58 C.)'are used in a pro: portion, for example of about50% or 60% to 75% or more of acetaldehyde, and preferably mixed withsome methyl or ethyl alcohol, cellular or tubular filaments can beproduced at a spinning temperature lower than that of the higher boilingsolvent, or anyhow not substantially higher; The lower the proportion ofaldehyde, the higher must be the spinning temperature for the productionof the same grade of cellular or tubular filament. The foregoing applieswhen, for example, a spinning solution of 20% to 30% concentration isused. Other concentrations of the spinning solutions will requirecorresponding conditions.

The difference of boiling points in the above case is about 37 C. If,instead of acetone, methyl or ethyl alcohol is used, the difference inthe boiling points is much greater and the production of cellular ortubular filaments is more pronounced, even at a somewhat lower spinningtemperature than the boiling point of the higher, boiling constituent.If a mixture of acetaldehyde and alcohol is used containing a certainquantity of acetone to increase its solvent properties, then a spinningtemperature intermediate between those previously indicated has to beemployed. It is possible to vary the spinning temperature as desired bya suitable addition of a solvent of intermediate boiling point to theacetaldehyde-alcohol mixture.

If instead of acetaldehyde, formaldehyde is used in combination withacetone, then, as formaldehyde is soluble in acetone, and the differencein boiling points is about 79 C., the formation of cellular or tubularfilaments takes place more readily at a temperature lower than or notsubstantially higher than the boiling point of acetone. In fact, whenformaldehyde is used, especially if large quantities of it are employedin the spinning solution, the temperature required for forming hollowfilaments is relatively low. It will be understood that this is stillmore pronounced when methyl alcohol or ethyl alcohol are used togetherwith the acetone, or when, I

as is preferred in practice, the formaldehyde is used in the form of aconcentrated solution in water. For instance 20 parts of a 40% solutionof formaldehyde may be used with 80 parts of acetone to form the solventmixture.

If instead of acetaldehyde o-r formaldehyde, methyl formate, having aboiling point of about 35 C. is chosen, the boiling point difference be-A tween that and acetone, viz. 23 C., is too small unless the quantityof acetone used is very small,

spinning temperature lower than the boiling point of the higher boilingsolvent and, in any 7 event, not substantially higher than the boilingpoint of the higher boiling solvent. It will be understood that thelarger the quantity of lower boiling solvent employed compared with thatof the higher boiling solvent, the lower the temperature at whichso-called hollow'filaments are produced. i

If however instead of alcohol, water is used with acetone as a solventfor celluloseacetate,

the temperature difference being 42 C., hollow filaments can easily beproduced, especially if, for example, based on the employment of 20-25%of water, the temperature chosen is under. the boiling point of water ornot-much higher. The greater the proportion of water added, the higheris the spinning temperature employed. The production of tubularfilaments is especially favourable when in addition to the water someother higher boiling solvents, such as diacetone alcohol, which easilymix with Water, are addedin proportions of about to 10% or even higher.

In combination with acetone, liquids such as cyclobutanone ormonomethylethyleneglycolether or diacetone alcohol may be used, insteadof water, in order to produce cellular or tubular filaments, in view ofthe substantial difference in the boiling points.

Instead of or together with acetone, ethyl formate or methyl acetate ormixtures thereof may be used in any desired proportion, as they havenearly the same boiling point as acetone.

In the foregoing description, the invention has been illustrated in itsapplication to cellulose acetate. Similar considerations apply to theproduction of voluminous filaments of a more or less cellular or tubularor continuously tubular structure by dry-spinning methods from othercellulose derivatives. For example, it is interesting to note that thesame principles exist in the case of solutions of nitrocellulose inmixtures of ether and alcohol; when the ether is present in the solventmixture in a proportion of more than 50 and preferably in the proportionof about 75%, cellular or tubular filaments are obtainable bydry-spinning at temperatures around, and at any rate not substantiallyhigher than, the boiling point of alcohol.

It is also understood that a plasticizer having a very high boilingpoint and therefore practically non-volatile may be incorporated in thespinning solution and remain permanently inthe filaments unless it isafterwards extracted by solvents or chemicals, as explainedbefore.

It shouldbe noted that, in using spinning solutions comprising a solventmixture containing 5 high and low boiling constituents as hereindescribed, if the spinning temperature be lower than those at whichcellular or tubular filaments are formed, the spinning operation willthen produce normal filaments in a manner substantially simi- 10.

lar to those described in U. S. Patents Nos. 1,- 566,384 and 1,669,158.

The following examples are given as an indication of how the inventionmay be carried into effect, but they are not to. be construed as in anyway limitative.

Example I A solvent mixture of acetone and acetaldehyde in equalproportions (boiling point diiference 37C.) is used to make a spinningsolution containing 26.1% cellulose acetate and the solution is spuninto air at a temperature of 72 C., filaments of a cellular characterbeing produced.

Example II I i Spinning is. carried out under the same conditions as inExample I, but into air at a temperature of 78? C, Almost completelytubular fila ments are produced) Example III A 20.7% solution ofcellulose acetate in a solvent mixture containing acetone andacetaldehyde in the proportions of 25/75 is spun into air at atemperature of 65 C. Again, almost completely tubular filaments areproduced.

Example IV Alcohol and methyl formate in the proportions of 30/70 areused to form a solvent mixture with a boiling point difierence of 43 C.,and a spinning solution containing 20.6% cellulose acetate in thesolvent mixture is spun into air at a temperature of 63 C. Cellularfilaments are produced.

Example VI Example VII 60 The spinning solution used in the two previousexamples is spun into air at a temperature of 95 C. to produce almostcompletely tubular filaments. 7 r

The foregoing examples and illustrations are 55 only explanatory and arenot limitative, and any solvents or combinations of solvents may beemployed which give the above-mentioned effects.

The spinning operation is preferably effected in relatively narrow cellsand/or when collectors are used in conjunction with the spinning jets,as described in the specification accompanying U. S. patent applicationS. No. 236,448 filed 29th November, 1927, and especially when thecollectors are associated or formed with heating devices.

What I claim and desire to secure by Letters Patent.is:-V-'

1. Process for the production of voluminous filaments of a cellular ortubular character, said process comprising dry-spinning a solution ofcellulose acetate dissolved in a solvent mixture containing alcohol and70% methyl formate at temperatures from 63 C. to 95 C.

2; Process for the production of voluminous filaments of a cellular ortubular character, said process comprising dry-spinning a solutioncontaining 20.6% cellulose acetate dissolved in a solvent mixturecomprising 30% alcohol and 70% methyl formate at temperatures from 63 C.to 95 C.

3. Process for the production of voluminous filaments of a cellular ortubular character, which comprises dissolving an organic derivative ofcellulose in a solvent medium containing at least two volatileconstituents whose boiling points difier by at least C., at least one ofwhich is itself a --solvent for the cellulose derivative, the quantityof the lower boiling constituents being from about to of the totalsolvent medium employed, and dry spinning the solution at temperaturesnear to, but, at the most, not substantially exceeding the boilingpoints of the higher boiling constituents.

4. Process for the production oi voluminous filaments of a cellular ortubular character, which comprises dissolving an organic deriva-- tiveof cellulose in a solvent medium containing at least two volatileconstituents whose boiling points difier by at least 40 C., at least onelower boiling constituent being itself a solvent for the cellulosederivative, the proportion of such lower boiling constituent being fromabout 50% to 75% of the total solvent medium employed, and dry spinningthe solution at temperatures near to, but, at the most, notsubstantially exceeding the boiling points of the higher boilingconstituents.

5. Process for the production of voluminous filaments of a cellular or'tubular character, which comprises dissolving cellulose acetate in asolvent medium containing at least two volatile constituents whoseboiling points difier by at least 40 C., at least one higher boilingconstituent and one lower boiling constituent being 20 themselvessolvents for the cellulose acetate, the quantity of the lower boilingconstituents being from about 50% to 75% of the total solvent mediumemployed, and dry spinning the solution at temperatures near to, but, atthe most, not sub- 25 stantially exceeding the boiling points of thehigher boiling constituents. Y

HENRY DREYFUS;

